Numerical investigation of the influence of frictional conditions in thread rolling operations with flat dies

Numerical simulation technology has become an important part of the process design stage in bulk metal forming operations. With increasing computing performance, three dimensional simulations within the product design process are thus becoming increasingly feasible. However, the modeling of friction within numerical simulations is still posing a challenge, especially in very friction sensitive processes, such as rolling of axisymmetric parts. Within the presented work, the process of rolling with flat dies with consideration of friction (according to Amontons-Coulomb) is simulated and analyzed. With the developed model, tribological loads as well as the influence of friction is investigated. These numerical findings are contrasted with experimental results obtained with an industrial forming machine. It is shown that the numerically obtained results are highly sensitive regarding numerical and physical contact modeling parameters. This is due in part to the highly varying frictional conditions (relative sliding velocity, contact normal stress) within the contact zone. Additionally, it is shown that the contact zone exhibits properties that favor static friction rather than sliding friction. This observation is especially important for an adequate empirical characterization of friction for thread and profile rolling processes.